Synergistic metal sequestrant

ABSTRACT

Mixtures of tris(hydroxymethyl)phosphine oxide, and nitrilotriacetic acid as well as the alkali metal salts thereof, exhibit marked synergism as sequestrant compositions over a broad pH range. The sequestrant compositions are useful as additives for detergents, metal cleaning baths, peroxide compositions and dyes. The chelate products are useful in the field of agriculture for the introduction of trace elements into plant life and especially in the treatment of iron chlorosis in plants.

United States Patent Carlson [151 3,655,573 1451 Apr. 11, 1972 [54] SYNERGISTIC METAL SEQUESTRANT [72] Inventor: Ronald R. Carlson, Lewiston, NY.

[73] Assignee: Hooker Chemical Corporation, Niagara Falls, N.Y.

[22] Filed: July 13, 1970 [21] Appl. No.: 54,662

Related US. Application Data [63] Continuation-in-part of Ser. No. 680,011, Nov. 2,

1967, abandoned.

521 u.s.c1 ..2s2/1s0,71/31, 71/54, 71/97, 252/102, 252/132, 252/137, 252/152, 252/186, 252/010. 11, 25 /010. 17, 260/534,

260/606.5 P [51] Int.Cl ..C02b 5/06,C11d 7/32,Clld 7/36 [58] Field of Search ..252/82, 86, 87, 137, 152, 175,

252/DlG. 11, 180, DlG. 17; 260/534, 606.5 P

[56] References Cited UNITED STATES PATENTS 3,578,708 5/ 1971 Carlson ..260/534 3,499,842 3/1970 Carlson ..252/180 3,477,953 1 H1969 Carlson ..252/175 2,583,891 1/1952 Schwarzenbach ..23/230 Primary Examiner-Leon D. Rosdol Assistant Examiner-Dennis L. Albrecht Attorney-Peter F. Casella, Donald C. Studley, Richard P. Mueller, James F. Mudd and William J. Crossetta 57] ABSTRACT 4 Claims, No Drawings SYNERGISTIC METAL SEQUESTRANT .RELATEDAPPLICATIONS This application is a continuation-in-part of Ser. No. 680,01 1, filed Nov. 2, 1967 now abandoned.

BACKGROUND OF THE INVENTION The invention relates to synergistic sequestrant mixtures, theirtuse and the chelated productsthereof.

The use of complexing agents which combine with metal ions in solution to form soluble complexes (which agents are commonly referred to as sequestrants) isof great importance in many industrial processesinasmuch as it may prevent undesired precipitation reactions from occurring. For example, sequestration of calcium is important in water treatment and in laundry solutions for controlling hardness of the water. Sequestration of the heavy metals such as copper and nickel is essential in-such areas as textile processing and metal cleaning and finishing. Not all sequestrants, however, are equally effective, their activity varying with their structures and the conditions under which they are used; for example, the common carboxylic acid sequestrants are often ineffective inpreventing ferric ion precipitation from alkaline solutions of pH greater than 8.

The commercial utilization of water-soluble chelating compounds in agricultural applications to provide trace elements -forplant. growth is well known. Likewise, the treatment of plants suffering from chlorosis as a result of growth in alkaline soils devoid of sufficient assimilatable iron is known. Various chelating agents have been employed in the past to correct iron deficiencies in plants, the water solubility of chelated metal ions affords the primary route for potential assimilation -intoa plant structure.

Ethylenediaminetetraacetic acid (EDTA) has been employed in the past for treatment of iron deficiencies of citrus treesunderacid conditions. The EDTA iron chelates are not stable in: neutral and alkaline media. The development of sequestrants which may be employed in acid media as well as alkaline :media is significant not only for agricultural applications, but for use in the detergent field, metal cleaning field, textileanddye industry and as stabilizers for organic and inorganic peroxides.

SUMMARY OF THE INVENTION In accordance with the instant invention, there is provided compositions of matter comprising tris(hydroxymethyl)phosphine oxide and at least one member. selected from the group consisting of nitrilotriacetic acid, and the alkali metal salts thereof, in mole ratio of about /90 to 90/10.

Furthermore, in accordance with the instant invention, there is provided a process for sequestering metal ions from aqueous solution over a pH range of about 4 to 11 by reacting the sequestrant mixture of this invention with metal ions.

Also, this invention provides novel compositions of matter comprising the sequestered metal ion derivatives of the sequestrant mixtures of this invention.

DETAILED DESCRIPTION OF THE INVENTION Mixtures of tris(hydroxymethyl)phosphine oxide (TI-1P0) and nitrilotriacetic acid (NTA) and its alkali metal salts unexpectedly display marked synergistic action as a sequestrant composition in mole ratios within the range from about 10/90 to 90/10, generally at a pH of from 4 to l 1.

The metal ions which may be sequestered by the composition of this invention are those cations having a valence of two or more, :such as the ions of chromium, copper, nickel, tin, aluminum, cobalt, platinum, palladium, rhodium, iridium, ruthenium, osmium, zirconium, hafnium, the rare earths such as gadolinium, europium, neodymium, the actinides such as uranium,.and especially iron in the ferric (Fe' state.

The-tris( hydroxymethyl)phosphine oxide component of the synergistic sequestrant mixture need not be introduced into an aqueous system for containing metal cations as such, because it may be formed in situ in known manner from various known precursors, such as tris(hydroxymethyl)phosphine and tetrakis(hydroxymethyl)phosphonium halide. Generally, at a pH above 7, the tretrakis(hydroxymethyl)phosphonium salts areconverted to the corresponding tris(hydroxymethyl)phosphine which undergoesoxidation to produce the phosphine oxide.

The nitrilotriacetic acid component of the sequestrant mixtures of this invention is preferably employed as its sodium (SNTA) or potassium (KNTA) salt to increase watersolubility.

The synergistic action of the sequestrant compositions of this invention varies with the pH of the aqueous system as well as with the mole ratio of the components in the mixture. With a 50/50 mole ratio of tris(hydroxymethyl)phosphine oxide to trisodium nitrilotriacetate the synergism of the sequestrant mixture toward ferric iron is evident at pH values from about 4 to about 11 while the effective pH range resides between about 6 to about 9 as the amount of tris(hydroxymethyl)phosphine oxide decreases to afford a 10/90 mole ratio of reactants. As the amount of tris(hydroxymethyl)phosphine oxide is increased from a 50/50 mixture of the two reactants to a /910 mole ratio, the effective pH range shifts to from about 7 to about 1 1.

The composition of this invention, when added to those solutions in which sequestration is desired, may be added as a solid or as a solution. If it is desired to add said composition as a solution, the composition may be dissolved in water. From about 0.001 percent to about 50 percent concentration (by weight) may be used, though it is preferred to use from about 0.01 to about 5 percent concentration (by weight), and it is even more preferred to use from about 0.1 to about 3 percent concentration (by weight).

It is preferred to use said compositions as sequestrants in aqueous solutions. When said composition is added to the solution containing metal ions to be sequestered, the temperature of said solution may be from about 0 to about centigrade, though it is preferred that said temperature be from about 20 to about 70 centigrade, and it is even more preferred that said solution be at ambient temperature.

The sequestrant mixture of this invention may be formulated either as an aqueous solution containing the two components in the desired ratio or as a solid mixture.

The sequestered iron chelate may also be employed as an aqueous solution or as a solid. The ferric iron chelate is soluble in aqueous alkaline solution in an amount exceeding 20 percent by weight, and contains more than 10 percent iron on a weight basis. Thus, when compared to the ferric iron chelate of EDTA, which contains a relatively low percentage of iron, 5-10 percent by weight, and which exhibits low solubility in alkaline solution, the sequestrant mixture of this invention presents decided advantages.

The solid ferric (Fe iron chelates of this invention are of the general composition Na,,[Fe (TI-IPO),,(NTA) in which n, x, y and z are numbers greater than 0, and may be prepared by mixing appropriate amounts of ferric chloride, sodium hydroxide, tris(hydroxymethyl)phosphine oxide (TI-1P0) and nitrilotriacetic acid (NTA) or a salt thereof in aqueous solution. After the reaction is complete, the solid chelate may be forced from solution by addition of a lower alkanol, such as ethanol or isopropanol. The isolated chelate is then dried and ground into a free-flowing brown powder.

EXAMPLE 1 To 37.7 grams of 50 percent solution of a 50/50 mole mixture of tris(hydroxymethyl)phosphine oxide and trisodium nitrilotriacetate monohydrate (0.09 moles) was added 50 grams of aqueous solution containing 14.5 grams (0.09 moles) of FeCl;,. Sumcient caustic was added to this solution to adjust the pH of the solution to 7. A clear, dark mahogany solution was now present above a layer of settled solids. The solution was decanted and to it was added 120 milliliters of absolute ethanol to fonn a two phase system. The phases were separated by decantation and the lower chelate phase was evaporated to dryness under vacuum (about 29 inches mercury absolute) at 50 C. Upon drying, a finely divided free flowing mahogany powder was obtained. Infrared analysis showed the product to contain both THPO and SNTA molecules. The product contained 22.6 percent Fe and was soluble in water in excess of 20 percent by weight. The pH of a 1 percent by weight aqueous solution of the product was 6.8. The chelate maintained its water solubility over a wide pH range upon addition of sodium hydroxide to the aqueous solution.

EXAMPLE 2 The procedure of Example 1 was repeated with the exception that isopropyl alcohol was used in place of ethyl alcohol to isolate the iron chelate product. The solid material recovered contained 12.9 percent iron and exhibited water solubility in excess of 20 percent by weight, maintaining its water solubility from pH 4 to about 12. The pH of a l percent solution was 6.7.

EXAMPLE 3 The sequestering efficiency of the sequestrant mixtures of this invention as well as the individual sequestrants were Table lContinued It is clear from the data presented in Table 1 that mixtures of tris( hydroxymethyl)phosphine oxide and trisodium nitrilotriacetate exhibit synergistic activity in the sequestration of the ferric ion at those pH values from 4-1 1 for the 50/50 mixture; from 6-9 for the 10/90 mixture; and from 7-1 1 for the 90/10 mixture.

The most pronounced synergistic activity of the sequestrant mixture of this invention is demonstrated by the 50/50 mixture at pH values from about 5 to about 10, while the l0/90 mixture exhibits its greatest synergistic activity at about pH 9, and the 90/10 mixture is most effective between a pH of about 8 to 10.

To further place the instant invention in perspective, the sequestering efficiencies of several known sequestrants for the ferric ion are presented in Table II. The abbreviations employed are as follows:

determined by titrating an aqueous solution 0.5 molar in EeCl Disodium iminodiacmw SDA dropwise into a stirred 50 gram aqueous solutlon containing Sodium tripolyphosphate STPP 0.5 gram of dissolved sequestrant until the end point was Twawdfumfthylme TA reached as observed by a perceptible permament haze in the il' z SED solution. The pH of the solution of dissolved sequestrant was Tn-mdium hydmyemyt initially adjusted to the desired point and maintained at the ethylened iaminetriacetate SHEDTA specified pl-l during the titration by addition of aqueous sodis gsgxg SNTMP um hydroxide as needed to control the hydrogen ion concen- Pentasodim: diefhylene 1311011. V triaminepentaacetate SDTPA TABLE II sequestering Efficiency sequestrant pH4 pH5 pHG pH? pHB pHQ pHlO pHll pH12 TABLE 1 pH THPO SNTA THPO/SNTA From a comparison of the sequestering efficiencies of the known sequestrants presented in Table 11, with the synergistic sequestrant mixture Tl-lPO/SNTA presented in Table I, it is apparent that the mixed sequestrant of the instant invention provides completely unexpected activity toward the ferric ion.

What is claimed is:

1. A composition of matter consisting essentially of tris(hydroxymethyl)phosphine oxide and a member selected from the group consisting of nitrilotriacetic acid, and an alkali metal salt thereof, in mole ratio of about 50/50 to /10.

2. A composition of claim 1 in which the mole ratio of tris(hydroxymethyl)phosphine oxide to nitrilotriacetic acid or alkali metal salt thereof is about 50/50.

3. A method for sequestering ferric ions in aqueous solution which comprises reacting said ferric ions at a pH of about 4-1 1 with the composition of claim 1.

4. A method for sequestering ferric ions in aqueous solution which comprises reacting said ferric ions at a pH of about 4-7 with the composition of claim 3. 

2. A composition of claim 1 in which the mole ratio of tris(hydroxymethyl)phosphine oxide to nitrilotriacetic acid or alkali metal salt thereof is about 50/50.
 3. A method for sequestering ferric ions in aqueous solution which comprises reacting said ferric ions at a pH of about 4-11 with the composition of claim
 1. 4. A method for sequestering ferric ions in aqueous solution which comprises reacting said ferric ions at a pH of about 4-7 with the composition of claim
 3. 